Tuber dormancy is an important physiological trait that impacts post-harvest storage and end-use qualities of potatoes. Overall, dormancy regulation of potato tubers is a complex process driven by genetic as well as environmental factors. Elucidation of the molecular and physiological mechanisms that influence different dormancy stages of tubers has wider potato breeding and industry-relevant implications. Therefore, the primary objective of this review is to present current knowledge of the diversity in tuber dormancy traits among wild relatives of potatoes and discuss how genetic and epigenetic factors contribute to tuber dormancy. Advancements in understanding of key physiological mechanisms involved in tuber dormancy regulation, such as apical dominance, phytohormone metabolism, and oxidative stress responses, are also discussed. This review highlights the impacts of common sprout suppressors on the molecular and physiological mechanisms associated with tuber dormancy and other storage qualities. Collectively, the literature suggests that significant changes in expression of genes associated with the cell cycle, phytohormone metabolism, and oxidative stress response influence initiation, maintenance, and termination of dormancy in potato tubers. Commercial sprout suppressors mainly alter the expression of genes associated with the cell cycle and stress responses and suppress sprout growth rather than prolonging tuber dormancy.

Sprout suppression is a crucial aspect of maintaining postharvest Solanum tuberosum (potato) tuber quality. 1,4-dimethylnaphthalene (DMN) has demonstrated effective sprout suppression during long-term storage of potatoes. Its mode of action, however, remains unknown, and previous studies utilizing single cultivars preclude identification of a common response to treatment. Thus, the goal of this study was to identify common transcriptomic responses of multiple potato cultivars of varying dormancy lengths to DMN exposure during two dormancy stages. RNA-seq gene expression profiling supported differing sensitivity to DMN treatment dependent upon cultivar and dormancy stage. A limited number of genes with similar expression patterns were common to all cultivars. These were primarily identified in ecodormant tubers and were associated with cell cycle progression, hormone signaling, and biotic and abiotic stress response. DMN treatment resulted in significant upregulation of members of ANAC/NAC and WRKY transcription factor families. Investigation of affected protein-protein interaction networks revealed a small number of networks responsive to DMN in all cultivars. These results suggest that response to DMN is largely cultivar and dormancy stage-dependent, and the primary response is governed by a limited number of stress and growth-related genes and protein-protein interactions.

The oomycete Plasmopara viticola, which causes downy mildew, is currently one of the most destructive pathogens affecting grape production. Although native to the eastern United States, P. viticola was introduced into Europe in the mid-to-late 1800s and is now found in virtually every grape-growing region of the world. Since its discovery, much effort has been made to understand the life cycle and infection process of the pathogen to develop more effective management practices. Widespread application of fungicides, especially those which have only one mode of action, has led to an increased occurrence of resistance to these treatments. Thus, with increased fungicide resistance and rising environmental concerns surrounding their use, traditional chemical management practices have begun to fall out of favor. Newer approaches, from targeted breeding utilizing quantitative trait loci to biological control agents, are continually being investigated and adapted to limit the damage caused by downy mildew. This review summarizes the current knowledge of the pathogen and methods of its control and explores potential avenues for future research focused on hypovirulence and biological control agents.

Gnomoniopsis castaneae is internationally recognized as a destructive pathogen of chestnut species. Primarily associated with nut rot, it has also been associated with branch and stem cankers of chestnut and as an endophyte of multiple additional hardwood species. The present study evaluated implications of the recently reported United States presence of the pathogen for domestic Fagaceae species. Stem inoculation assays of Castanea dentata, C. mollissima, C. dentata × C. mollissima, and Quercus rubra (red oak) seedlings were utilized to examine the cankering ability of a regional isolate of the pathogen. The pathogen induced damaging cankers in all assessed species and significant stem girdling in all chestnut species. No previous study has associated the pathogen with damaging infection in Quercus species, and its presence in the United States has the potential to compound ongoing chestnut recovery programs and oak regeneration problems within forest systems.

Gnomoniopsis castaneae is an important, destructive pathogen of Castanea species, initially identified as the primary agent of nut rot in Europe and Oceania. Although a decade of research has focused almost exclusively on its association with and activity in chestnuts, it has been identified as a mild pathogen or endophyte in multiple other hardwood species, whose roles as potential reservoirs and hosts have remained unexplored. Although the origin of the disease is unknown, it is thought to be a ubiquitous endophyte that has potentially shifted to pathogenic activity as a result of global climate change. Yet there is evidence of the expansion of the range of the pathogen as it continues to be identified in new regions, suggesting some degree of introduction is occurring. Its recent discovery in the United States brings a new urgency to the need to understand the full range and epidemiology of G . castaneae and to examine potential methods of detection and mitigation.

Anthropogenic climate change is affecting virtually all ecosystems across the globe. Some of the noticeable effects of the changing climate are the shifting of frost dates in the fall and spring, and how warm temperatures are distributed throughout the year. The degree to which an ecosystem is affected by these changes depends upon many factors, including where the ecosystem is located and what regional variabilities in climate surround that ecosystem. One ecosystem that experiences a unique microclimate is the region surrounding Lake Erie, the southernmost Laurentian Great Lake. Using historic climate data dating from 1948 to 2017, we set out to determine how changes in temperature and frost dates differ between the coastal and inland regions of the southern coast of Lake Erie, and to hypothesize as to why these effects may be occurring differently between these regions. We found that, for both coastal and inland regions, the first frost in the fall has begun later, while the last frost in the spring has begun earlier, leading to both regions experiencing longer frost-free seasons. However, although both regions have experienced these shifts, the rate at which these shifts occurred differed between the coastal and inland regions. The average date that the frost events occurred also differs between the two regions. It was also found that average temperatures have been increasing for each region, primarily in coastal regions, due to increased minimum temperatures over time. The results from this study highlight the importance of regional climate variability in large-scale climatic studies.

Commercial storage of potatoes often relies on the use of sprout inhibitors to prolong storage and reduce spoilage. The compound 1,4-dimethylnaphthalene (DMN) has seen increase application as a sprout inhibitor in the potato industry as older chemistries are being phased out. The mode of action of DMN is poorly understood as is the sensitivity of potato tissues to this new class of inhibitor. During storage potato tubers transition from a state of endo-dormant to eco-dormant and it is not known if the DMN response is consistent across this developmental transition. RNA-seq gene expression profiling was used to establish if stored potato tubers (Solanum tuberosum cv La Chipper) have differential sensitivity to DMN as tubers age. DMN was applied at three different times during storage; just after harvest when tubers are in endo-dormancy, midwinter at early eco-dormancy, and in spring during late eco-dormancy when sprouting was prevented via exposure to cold storage temperatures. Changes in gene expression were lowest during endo-dormancy while midwinter and spring treatments exhibited a greater and more diverse expression response. Functional analysis of differential gene expression demonstrated gene sets associated with DNA replication, cell division, and DNA methylation are suppressed after DMN treatment. However, gene sets associated with salicylic acid, jasmonic acid, abiotic and biotic stress responses are elevated by DMN only after endodormancy terminates. Gene clusters associated with pathogenesis related proteins PR-4 and PR-5 are also upregulated in response to DMN. These results indicate that DMN sensitivity changes as potato tubers age and transition from endo-dormant to eco-dormant in storage and the overall response is a shift in gene classes that regulate growth and response to stress.

The compound 1,4-dimethylnaphthalene, originally isolated from dormant potatoes, is currently in use as a commercial sprout inhibitor. Growers and processors report a reduction in fungal infections in potatoes treated with DMN resulting in increased yields. To assess the effects of DMN on fungal growth a culture of Fusarium oxysporum was isolated from potato tubers and identified via DNA fingerprinting using the 18ITS ribosomal region. Growth of F. oxysporum was inhibited by 31% after four days of exposure to DMN but overall rate of spore germination was not affected by DMN treatment. The growth of additional fungi, including Alternaria alternata, Aspergillus niger, Epicoccum nigrum, Gnomoniopsis smithogilvyi, Phoma medicaginis, and Pythium ultimum was inhibited by DMN as was suppression of sporulation in A. niger. These results suggest that DMN is fungistatic at the application levels examined.

Alternaria alternata is a pathogenic fungus known to cause leaf spot in many plant species such as apples, purple coneflower, onions and many others. Actinidia arguta (hardy kiwifruit) is an alternative crop which has commercial potential in the United States. Field trials of A. arguta, located at Lake Erie Regional Grape Research and Extension Center, presented leaf lesions which suggested the presence of a pathogen. Leaf samples were taken from multiple symptomatic vines and allowed to incubate in empty sterile petri dishes. Symptomatic sections, approximately 1 cm2, were cut from the leaves and placed onto fresh potato dextrose agar (PDA) plates and incubated at 25°C for three days. Several fungal species were present on the plates with one fungal species common among all leaf samples plated. All visibly different species were isolated onto separate PDA plates, incubated, and re‐plated until purified cultures were obtained. PCR amplification of the 18 ITS region was accomplished using degenerate primers and DNA products were identified using Sanger sequencing. Resultant sequences were analyzed with BLASTn against the NCBI database. Cultures of A. alternata were identified as present on multiple leaf lesions. Established cultures were treated with 1,4‐dimethylnaphthalene (DMN) in a 9.5 Liter BBL GasPak chambers for two days. Mycelial growth was inhibited by DMN relative to control cultures. This is the first report of A. alternata isolated from the leaves of A. arguta and a demonstration that DMN can inhibit growth of this fungal species.Support or Funding InformationFunded in part from a grant from the 1,4‐Group of Meridian, ID and the Behrend College Undergraduate Research FundThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

The compound 1,4‐dimethylnaphthalene (DMN) was originally isolated from dormant potatoes and is currently being used as a commercial sprout inhibitor. In order to determine how the microbiome of potatoes is affected by the compound, two fungal species were grown and quantified under control and DMN conditions: Pythium ultimum and Aspergillus niger. These two fungal species are commonly found on the surface of potatoes and can result, respectively, in Pythium leak and black rot on onions. Fungal cultures were obtained from ATCC (P. ultimum: 58811, A. niger: 16888) and grown on potato dextrose agar (PDA). Mycelial cultures were grown in 9.5 Liter BBL GasPak chambers, exposed to either mineral oil (control) or DMN for two days. The mycelial mats exhibited reduced growth under DMN conditions in comparison to controls. DMN treatment of mature A. niger cultures also prevented sporulation. This indicates that DMN displays fungistatic properties but does not function as a fungicide towards P. ultimum and A. niger. In order to determine how DMN affects the gene expression of these fungi, RNA sequences will be collected and gene expression will be observed between control and DMN treatments.Support or Funding InformationSupported in part by a grant from the 1,4‐Group of Meridian, ID and the Behrend College Undergraduate Research FundThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

The compound 1,4‐dimethylnaphthalene (DMN) is a natural growth inhibitor produced in dormant potatoes. It prevents potato tubers from sprouting by halting cell division. Recent studies have shown DMN prevents the growth of microbiomes present on the surface of stored potato tubers. However, the effect of DMN on small RNAs has not been yet investigated. The molecular miR166 is a highly conserved class of microRNA in many plants. It is found in meristems, and it modulates transcripts of the III homeodomain‐leucine zipper family genes to control plant growth. High expression of miR166 in Arabidopsis thaliana downregulated transcription factors such as Phavulota (PHV) and Phabulosa (PHB), suppressing growth of various parts of the plant. Therefore, we hypothesized that DMN increases miR166 expression to inhibit sprouting. Potatoes were exposed to DMN or nuclease‐free water (control) for three days. Meristems were isolated, frozen in liquid nitrogen, and stored at −80 C. RNAs were isolated using mirVana kit (Thermofisher.com). Total RNA was measured and converted into cDNAs using stem‐loop primers, specifically made for mir166. TaqMan qtPCR was used to quantify the expression of mir166 in control and treated samples. The results obtained from TaqMan qtPCR showed that the expression of miR166 in the treated sample was equivalent to the control sample, suggesting that DMN did not change miR166 expression in dormant potatoes. Further experiments will determine if DMN alters miR166 expression in potatoes after dormancy terminates.Support or Funding InformationSupported in part by a grant from the 1,4‐Group, Meridian, IDThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Prolongation of storage via temporary meristematic sprout inhibition has effectively been carried out in tubers after brief exposure to 1,4‐dimethylnaphthalene (DMN), a compound naturally abundant in the tissues of dormant potatoes. Not only does DMN suppress meristematic growth, but studies have shown that DMN greatly impacts the microbiome on the surface of potatoes, especially with regards to species diversity. Among the diverse microbiome population is Fusarium oxysporum, a particular strain of pathogenic fungus responsible for the plant disease fusarium wilt. F. oxysporum was successfully isolated from the surface of a tuber using the fusarium selective media Nash‐Snider, to which cultures were transferred and maintained on nutritionally complex potato dextrose agar plates. DNA sequencing using selective primers NL1, NL2, ITS1F, and ITS2R confirmed the fungus to be F. oxysporum. A single spore isolation technique was utilized to record the number and growth response of spores treated with DMN vs spores treated with water (control). Single spore isolate plates were contained in vacuum sealed chambers and incubated at a constant 22C while exposed to 7.5ul DMN via aerosol dispersion for four days. After a day of rest, the spores on each plate were measured and counted. The results concluded spores exposed to DMN showed slower diameter growth than those treated with water. Knowing the effect of DMN on F. oxysporum is critical in controlling and preventing harvest loss brought on by fusarium wilt. In an attempt to gain more insight on the specificities of the DMN‐fungal conundrum, further studies are still being conducted.Support or Funding InformationSupported in part by a grant from the 1,4‐Group, Meridian, IDThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

It has been shown in recent studies that 1,4‐dimethylnaphthalene (DMN) can halt cell division in tuber meristems of Solanum tuberosum. By preventing cell division, DMN can prevent sprouting and prolong storage. RNA sequence data of potatoes treated with DMN revealed that the gene encoding for pathogenesis‐related protein 4 (PR‐4) is significantly induced in response to DMN. The level of PR‐4 gene expression increased by three‐fold in the fall and winter and by six fold in the spring, which is during late storage and the tissues are no longer dormant. This demonstrates that dormant potato tubers are recalcitrant in response to DMN induction of PR‐4. The PR‐4 protein belongs to a large family of plant host proteins triggered in response to pathological situations, such as bacteria or virus invasion. Members of PR protein family have different functions. PR‐4 is specifically involved in wound response, and it has both RNase and DNase activity. Further experiments are being conducted to determine the level of gene product for PR‐4 in response to DMN. Currently, it is unclear how the expression of PR‐4 relates to the suppression of cell division in potato meristems.Support or Funding InformationSupported in part by grant from the 1,4‐Group of Meridian, IDThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

The agricultural compound 1,4‐dimethyl naphthalene (DMN) can be used to inhibit sprouting and prolong the storage of Solanum tuberosum. Potatoes treated with DMN exhibit characteristics that enable greater crop yields, including pathogen response, water retention, and greater shelf life. However, the molecular mode of action as to how DMN brings about these changes within the potato is not well understood. Two years of RNA‐seq data demonstrate extensive changes in gene expression within potato samples treated with DMN at different times throughout the year. Significant changes have been highlighted among a particular group of genes located on chromosome one. This group of genes codes for a pathogenesis‐related‐protein, PR5. As an extracellular protein, PR5 has an extensive signal transduction that responds to pathogens and abiotic stress. Among the PR5 family is a group of cytosine‐rich proteins called osmotins. Osmotin is a ubiquitous protein among several plant species and serves as a useful molecular marker for the systemic acquired resistance response, which is analogous to the innate immune system in plants. Gene expression measurements were taken over a six month period, during which dormancy was naturally breached. RNA‐seq data reveals 2‐3 fold increases between measurements taken before and as dormancy was breaking. After dormancy was breached, PR5 gene expression continued to rise significantly in comparison to previous measurements. These trends in gene regulation imply that the PR5 expression proceeds concurrently with sprout growth in DMN treated potatoes, and are related to the systemic changes seen from the outside of the potato. Phylogenetic analysis reveals the PR5 genes with the greatest changes in expression (7865 and 7870) demonstrate the greatest homology among their transcripts. Current analysis is being done using qPCR primers directed towards genes 7865 and 7870. Expression levels from qPCR should mirror the RNA‐seq data, in addition to demonstrate more immediate expression following DMN treatment. It has been hypothesized that gene expression spikes in prominent PR5 genes (7865 and 7870) will signify a broad molecular mode of action DMN plays inside S.tuberosum.Support or Funding InformationSupported in part by a grant from the 1,4‐Group, Meridian, ID.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Prevention of sprouting in stored potato tubers is a major concern for the agricultural and food industries. The compound 1,4‐dimethylnaphthalene (DMN) has been shown to prevent premature sprouting when fogged onto the surface of potato tubers. Treatment of Saccharomyces cerevisiae cultures with DMN resulted in a temporary suppression of growth. Based on that data we speculate that treatment of stored potato tubers with DMN would result in sprout suppression as well as alteration of fungal communities on the surface of potato tubers. The treatment of potatoes was done with DMN or sterile water (control) for two days. The surface of the potatoes consisted of 4.2 ppm of DMN residue after treatment. Periderm (2 cm) samples were quickly frozen in liquid N 2 and stored at −80°C after the treatment. DNA was isolated from frozen tissues using a Power Soil DNA Isolation Kit (mobio.com). Total DNA was measured and prepared for PCR using primers specific to the ITS regions of fungi (F). PCR products were evaluated using gel electrophoresis and sequenced using Illumina technology (Penn State Nucleic Acid Facility). A total of 3.7 million DNA sequences were analyzed using the Mothur (v1.36) software package to determine fungal diversity by alignment to the silva.eukarya.fasta database. Among all samples there were 1124 operational taxonomical units (OTU). It was determined that there is a greater fungal diversity on the control tissue than the DMN treated tubers. This data suggests the DMN alters the fungal diversity on the surface of potato tubers. Support or Funding Information Penn State Behrend, 1,4‐Group

The compound 1,4 dimethyl naphthalene (DMN) has been shown to be an effective inhibitor of sprouting when applied to stored potato tubers. DMN has also been shown to be a growth inhibitor of bread yeast (Saccharomyces cerevisiae). Thus, we hypothesize that DMN would alter the micro‐biome that exists on the surface of stored potato tubers following treatment for sprout suppression. Potatoes were cut in half with one piece treated with DMN and the other piece exposed to an identical volume of sterile water as a control. DMN surface residues were determined after 48 hrs of treatment. The amount DMN residue deposited on the uncut surface was 4.2 ± 1.1ppm, which is similar to levels used for sprout inhibition. Deposition of DMN on the cut surfaces was much lower (1.54 ±0.65 ppm (n=33)), which may be a function of the low solubility of DMN in water. Periderm disks from the cut and uncut tuber surfaces were then frozen in liquid nitrogen and stored at −80°C. A Power Soil DNA Isolation Kit (mobio.com) was used to isolate DNA from the frozen samples. DNA was quantified and then used for PCR using primers specific to bacterial species (V3, V4). PCR products were quantified, checked by gel electrophoresis and then sequenced using Illumina technology. The total number of sequences generated was 3187447. The software program Mothur (v1.36) was used to determine the level of microbial diversity demonstrating that there were 20527 unique sequences that functioned as operational taxonomic units. Homogeneity of molecular variance (HOMOVA) was used to analyze the population of bacteria. There was no statistical difference between the cut and uncut surfaces of potato tubers (p=0.452). However, our alpha analysis for the skin of the potato did show a difference (p=0.017) between populations of uncut control and uncut DMN. Also, comparing alpha diversity between DMN cut and uncut, there appears to be a difference in population (p‐value=0.0001). We conclude that DMN does have an impact on the microbial diversity on potato tubers.Support or Funding InformationPenn State Behrend, 1,4‐Group

Application of the compound 1,4-dimethylnaphthalene (DMN) has been found to reduce premature sprouting in stored potato tubers. The mechanism of action for DMN has yet to be elucidated but transcriptional changes are known to occur following exposure. In this study non-dormant potato tubers ( Solanum tuberosum L., cv. Russet Burbank) were treated with varying amounts of DMN resulting in an increasing residue on the tuber surface. RNA sequencing was used to measure transcriptome changes in excised meristems from tubers having increasing DMN exposure. Treatment of tubers with DMN that resulted in surface residue levels greater than 2 ppm was associated with a decrease in 45 transcripts that encoded for proteins linked with plastid development and function and an increase in the expression of 15 transcripts that encoded for WRKY-type transcription factors. qt-PCR analysis showed that repression of plastid transcripts appeared to recover 7 days after DMN exposure but induction of WRKY transcripts was maintained up to 35 days post treatment. The data suggests DMN may inhibit plastid development short term but also results in long-term changes in some regions of the transcriptome.

Potato is the third most important food crop in the world and is an excellent source of dietary calories, vitamins, and minerals. At harvest and for an indeterminate period thereafter, potato tubers are in a state of physiological dormancy and will not sprout. Tuber dormancy is lost during storage in a cultivar-and environmentally dependent manner. The onset of sprouting, which follows the loss of tuber dormancy, results in numerous biochemical changes that are detrimental to the processing and nutritional qualities of potatoes.

Cytokinin, auxin and gibberellin contents in resting and wound-responding potato tubers have not been fully determined and coordinated with wound-healing processes. Using a well-defined wound-healing model system, hormone content and expression of genes associated with hormone turnover were determined in tubers following wounding. Changes in hormone content were coordinated with: (I) formation and completion of the wound closing layer (0-5/6 days), and (II) initiation of phellogen and wound periderm formation (∼ 7 days). Quantifiable amounts of biologically active cytokinins (Z, DZ and IP) were not detected in resting or wound-responding tubers. However, the precursor IPA and catabolic product c-ZOG were found in small amounts in resting and wound-responding tubers. Wound-induced activation of cytokinin biosynthesis was suggested by an increase in t-ZR and c-ZR content at 0.5 days and large increases in IPA and c-ZR content by 3 days and throughout 7 days after wounding suggesting roles in II, but little or no role in I. Expression of key genes involved in cytokinin metabolism followed similar profiles with transcripts decreasing through 3 days and then increasing at 5-7 days after wounding. Both free IAA and IAA-Asp were present in resting tubers. While IAA-Asp was no longer present by 3 days after wounding, IAA content nearly doubled by 5 days and was more than 4-fold greater at 7 days compared to that in resting tuber (0 day) suggesting roles in II, but little or no role in I. Gibberellins were not present in quantifiable amounts in resting or wound-responding tubers. These results suggest that bio-active cytokinins are wound-induced, but their residency is temporal and highly regulated. The transient presence of active cytokinins and corresponding increases in IAA content strongly suggest their involvement in the regulation of wound periderm development. The absence of gibberellins indicates that they are not a regulatory component of wound-healing processes.